Analysis and prospects of the function, mechanism and environmental protection of color-fixing agents
Dye-fixing agent is one of the important additives in the printing and dyeing industry. Its main function is to improve the color fastness of dyes on fabrics to moisture treatment. It can form insoluble colored substances with dyes on fabrics to improve the color’s fastness to cleaning, perspiration, and sometimes sunlight.
Plants in nature bloom with colorful flowers. They were originally used to attract insects for pollination, but unexpectedly they attracted people’s liking, and thus their clothes were dyed with various colors. A bright color. The coloring of fabric materials is usually done in a dye bath to chemically or physically combine the dye with the fibers, or to generate insoluble colored substances on the fibers. The resistance of dyes to washing, sunlight, friction and other properties on fibers is called color fastness.
Reactive dyes chemically react with fibers when coloring, forming a covalent bond between the two, so they are also called reactive dyes. In 1956, the UK first produced the procion brand of reactive dyes. Reactive dyes have broad chromatograms, bright colors, excellent performance, and strong applicability, but they also have shortcomings such as insufficient fastness to sweat, moisture, and daily wear. The function of the fixative is to improve the solidity rate and wet processing fastness of the dye during the coloring process.
1. Coloring mechanism of reactive dyes
1. Structure of cotton fiber
Mature cotton fiber is mostly composed of cellulose. Cellulose is a natural polymer compound and a polysaccharide substance. Its molecular formula is C6H10O5. The constant periodicity of the cotton fiber macromolecule structure constitutes the spatial structure of the cellulose macromolecule. The functional group of cellulose macromolecules is a strong group, and the hydroxyl group is a hydrophilic group, so cotton fiber has the ability to absorb moisture.
The groups of cotton cellulose molecules participating in the nucleophilic reaction are C6, C2 and C3. C6 is a primary hydroxyl group, and its reaction rate is fast; C2 secondary hydroxyl group is inherently reactive, but has greater steric hindrance, so the reaction rate is lower than C6; C3 is a secondary hydroxyl group, and its steric hindrance is also greater. And it will form intramolecular hydrogen bonds, so the reactivity is relatively low.
2. Structure of reactive dyes
Reactive dyes are composed of color bodies, active groups, linking groups, and water-soluble groups. The active groups in the molecular structure can form covalent bonds with the hydroxyl groups on cellulose fibers and the amino groups on protein fibers.
Active groups can be divided into X-type, K-type and KN-type according to their reactivity. The X-type reactive group has strong reactivity, low stability, and is easy to hydrolyze, but the dyeing speed is fast and is suitable for low-temperature coloring. The K-type active group has weak reactivity and high stability, and is suitable for high-temperature coloring. The performance and coloring conditions of KN-type reactive dyes are between those of X-type and K-type. However, in order to improve the color fixation rate, single reactive dyes are generally not used, but dual reactive dyes such as M type and B type are used.
3. Reactive dye coloring process
When reactive dyes are used for coloring, the reactive dyes first dissolve in water, and the dye and moisture enter the fiber at the same time and adhere to the fiber. The degree of absorption of the dye in the dye liquor depends on the affinity of the dye and the electrolyte concentration in the dye liquor. The dye also reacts chemically with the fiber during the diffusion of the dye into the fiber.
Cellulose fibers are inactive in neutral media. The dye and fiber are only in an attachment relationship. Only when cellulose fibers are in alkaline media can they be covalently bonded. This is because the cellulose fibers form negative ions at this time, and their ion concentration increases as the pH increases. It is also seen here that the cellulose fiber acts as a weak acid and neutralizes with the alkali agent.
2. Fixing agent requirements
The fixing agent should reduce the solubility of the dye. The following requirements are required for the fixing agent:
1. Can improve the dye fastness of dyed fabrics.
2. Maintain the original color and fastness of the dyed fabric.
3. No harm to human body.
4. Does not affect the environment and has good biodegradability.
5. Cheap and easy to obtain, and the supply of raw materials is domestic.
6. Suitable for padding and dipping methods, easy to use and not limited by technology.
The book also describes the current status of color-fixing agents, classification of color-fixing mechanisms, types of aldehyde-free color-fixing agents, and functional water-based polyurethane color-fixing agents. Among them, the color-fixing mechanism In addition, the color-fixing agent and the dye are used to generate an insoluble lake, the color-fixing agent forms a film on the surface of the fiber, the color-fixing agent cross-links the hydroxyl groups on the fiber, the hydrogen bonding attraction is used to increase the color-fixing strength, the acid resistance is improved, and the smoothness is used to improve the perspiration fastness. Eight categories will be introduced: agents to improve friction dyeing fastness, ultraviolet absorbing groups to improve sun-resistant dyeing fastness, and chlorine-resistant substances to improve chlorine-resistant dyeing fastness. The formaldehyde-free color fixing agent is also divided into five main types: non-reactive agarose resin, reactive compound or reactive resin, ammonium reactive resin or compound, ammonium salt polymer, quaternary ammonium salt Reactive polymers provide a positive explanation.
Conclusion:
In recent years, in order to protect the ecological environment, many manufacturers have worked hard to lament that some of them are environmentally friendly and aldehyde-free. However, they still cannot meet the requirements in terms of wet treatment dyeing fastness. Nowadays, everyone is emphasizing green and low-carbon. Originally, dyeing fabrics with bright colors will easily pollute the environment, but consumers prefer flowers in green. Therefore, our printing and dyeing science and technology workers must continue to work hard to develop both A color fixing agent that is environmentally friendly and keeps fabrics from fading.
The above information comes from technical production knowledge in fabric additive books. If actual operation is required, the operator needs to think on his own. Our company does not bear any legal responsibility.
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